domino theory

domino theory, the notion that if one country becomes Communist, other nations in the region will probably follow, like dominoes falling in a line. The analogy, first applied (1954) to Southeast Asia by President Dwight Eisenhower, was adopted in the 1960s by supporters of the U.S. role in the Vietnam War. The theory was revived in the 1980s to characterize the threat perceived from leftist unrest in Central America.